1. Field of the Invention
The present invention relates to a method of producing an electrophotographic photoconductor and an electrophotographic photoconductor produced by the method (also referred to simply as “photoconductor” and “production method”), in particular, to a method of producing an electrophotographic photoconductor mounted on electrophotographic apparatuses such as copiers, facsimile machines, and printers, and an electrophotographic photoconductor produced by this method.
2. Description of the Related Art
An electrophotographic photoconductor has a basic structure comprising a conductive cylindrical substrate and a photosensitive layer including a charge generation substance, a charge transport substance, and a resin binder formed on the substrate. A material primarily used for a cylindrical substrate of a photoconductor is an aluminum alloy, specifically of material code 6063 (prescribed in Japanese Industrial Standards) containing additives of silicon and magnesium, or 3003 containing additives of iron and manganese. The aluminum alloy is generally cast after the steps of welding, composition adjustment, and removing impurities such as oxides, and formed into a cylindrical shape by hot extrusion. Then, the aluminum cylinder is given improved dimensional accuracy by cold drawing and cut using a turning tool of sintered diamond to obtain a cylindrical substrate having desired dimensions (hereinafter referred to as a “raw drum”).
In the cutting process, a mist of cutting oil (electrical discharge machining oil or kerosene) is sprayed onto the surface of the raw drum to cool the tip of the tool and control the direction of scattering of cut chips. As a result, a large quantity of the cutting oil adheres to the surface of the raw drum. Since a photoconductor is produced by coating this surface of the raw drum with a photosensitive layer, the cutting oil adhered to the drum in the cutting process must be removed in a cleaning process before a process of coating with the photosensitive layer.
There are known techniques for improving aluminum raw drums used in photoconductors. Japanese Unexamined Patent Publication No S63-300277 discloses a technique for obtaining a photoconductor drum exhibiting good electrical characteristics by using a photoconductor drum substrate composed of an aluminum alloy containing a specified quantity of nickel. Japanese Unexamined Patent Publication No. S63-179037 and Japanese Unexamined Patent Publication No. S63-179038 disclose techniques for obtaining an aluminum alloy cylinder exhibiting good surface smoothness by regulating iron content and nickel content, respectively, in the aluminum alloy. Japanese Unexamined Patent Publication No. H7-234531 discloses in paragraph [008] thereof that a conductive substrate composed of an aluminum alloy containing iron in a specified quantity suppresses the number of etching pits generated in the process of cleaning with weak alkaline detergent. Japanese Unexamined Patent Publication No. H6-236059 discloses a technique for obtaining a photoconductor with good image quality by using a conductive substrate produced by controlling the surface roughness in the processes of extrusion, drawing, and pressurized polishing.
In the above-mentioned step of cleaning a raw drum, chlorine-containing organic solvents have heretofore been used, represented by trichloroethylene, dichloromethane, and flon, which exhibit high polarity and strong dissolving ability. Use of these organic solvents was stopped recently because of heavy environmental loading. Instead, so-called aqueous cleaning agents such as neutral detergent and alkaline cleaning agents are being used.
However, problems that occur in the use of aqueous cleaning agents, but not in the process of cleaning with conventional organic solvents, have become apparent. Aluminum alloys primarily used in a raw drum contain inorganic additive elements of silicon and magnesium in order to facilitate cutting, so the aluminum alloys include crystallized deposits or precipitations of intermetallic compounds such as Mg—Si, Fe—Si, Fe—Al—Si or the like having a diameter of 5 to 20 μm. In an aqueous cleaning agent, aluminum around the crystallized deposits dissolves by etching, generating an etching pit. A study by the inventor has further clarified, as described later, that this etching occurs not only when dipping in high pH cleaning agents but also in pure water, resulting in the generation of etching pits.
In these etching pits, a small amount of cleaning agent used in a cleaning process or water used for rinsing the agent generally remains. A photosensitive layer normally comprises a CGL (charge generation layer) and a CTL (charge transport layer) sequentially applied and formed on a raw drum through a UCL (undercoat layer). After applying each layer, heated drying is conducted at a temperature in the range of 80 to 150° C. to dry the applied layer. The undercoat layer often contains filler material of TiO2 inorganic pigment dispersed in the layer. In such a case, due to the water component or the like remaining in an etching pit, aggregation 14 of filler material 13 in the coating liquid 12 of undercoat layer occurs in the etching pit 11 as shown in FIG. 7. It has been clarified that this aggregation causes a printing defect, which is fatal to a photoconductor. The symbol 15 in FIG. 7 indicates a crystallized deposit in the aluminum alloy.